Aberrant activation of the TAL1/SCL gene has been involved in majority of T cell acute lymphoblastic leukemia (T-ALL). As a hematopoietic-specific basic helix-loop-helix transcription factor, TAL1 is essential for hematopoietic stem cell renewal and lineage development during normal hematopoiesis. Given its relevance to normal hematopoiesis and T-ALL, understanding the transcriptional control of this transcription factor will elucidate the molecular mechanisms underlying the control of normal hematopoiesis and leukemogenesis. Several lines of evidence have established that TAL1 associates with transcriptional coactivators and corepressors which differentially affect TAL1's function in erythroid differentiation. Hence, we hypothesize that histone modifying enzymes regulate TAL1-mediated transcriptional control during hematopoiesis and their misregulations would contribute to the development of T-cell leukemia. In this application, we focus on investigating how the opposite histone modifying enzymes that we have identified as TAL1-associated cofactors regulate TAL1 function in hematopoiesis and leukemogenesis. The specific aims of this research proposal are: 1) Elucidate the biological function of histone demethylase in the control of TAL1-mediated transcription and hematopoiesis;2) Analyze the role of histone methyltransferase in TAL1-mediated transcriptional regulation during erythroid differentiation;3) Understand the molecular basis of histone modifying enzymes in TAL1-induced normal hematopoiesis and leukemogenesis. By completing the proposed research, we expect to further understand how TAL1- directed transcriptional activity contributes to normal hematopoiesis and leukemic transformation. We will also gain knowledge on the role of TAL1-associated histone modifying enzymes in these processes. This information will eventually help to design new therapeutic approaches to treat leukemia. Moreover, the study will shed light on the control of transcription factors on hematopoietic stem cell growth and differentiation. Project Narative: Transcription factor TAL1/SCL is critical for the formation of normal blood cells and is frequently associated with a specific form of leukemia, T cell acute lymphoblastic leukemia (T-ALL) which is a malignant disease with very few effective treatments. In this proposal, we will explore how TAL1 regulates the formation of blood cells and the development of leukemia. These studies will provide novel insights into TAL1 function in the regulation of blood cell development and will help to design new therapeutic approaches to treat leukemia.